Low-impact delivery system for in situ treatment of contaminated sediment

ABSTRACT

An agglomerate for use in economical bulk treatment of contaminated sediments with minimal environmental impact is formed from a sorbent, bentonite clay and sand. The agglomerate has sufficient density so as to sink through a water column into sediment below the water column and is still sufficiently light as to be capable of mixing with the sediment when subjected only to bioturbation. The agglomerate can be formed into pellets and applied to a water column over contaminated sediment by broadcast methods, so as to permit economical remediation of contaminated sediment with negligible environmental impact.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 6/852,628, filed Oct. 18, 2006, which is herebyincorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was supported in part by government funding awarded bythe Department of Defense and the United States Environmental ProtectiveAgency, specifically contract numbers W912HG-06-00022, and EP-D-06-029.The U.S. Government has certain rights in this invention.

APPENDIX

Not Applicable.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the field of clean-up ofcontaminated bodies of water, and, more particularly, to a deliverysystem for treatment of contaminated underwater sediment in situ, havinglow impact on the benthic community.

To date, the most commonly considered alternatives for contaminatedsediment management are (1) dredging and placement in confined disposalfacilities (CDFs) or hazardous waste landfills and (2) capping, anoption for containment in engineered subaqueous sites. However, eitheroption is expensive and requires large-scale material handling andlong-term management. In addition, dredging operations can causetemporary high levels of contaminants in the water column (the wateroverlying the sediment in a lake, harbor, river, or other water body)and surficial sediments due to re-suspension of buried contaminatedsediments and release of pore water. Further, all known sedimenttreatment technologies will leave residual contaminants. Innovativeengineering solutions to the problem of persistent organic contaminantsin aquatic food webs require rethinking of the existing remediationparadigm of “dredge-and-landfill.” Although several researchers havefound promising amendment materials for sequestration of organic andmetal contaminants in sediments, to be successful the practicalapplication of these approaches in the field require low-cost andlow-impact delivery approaches.

SUMMARY OF THE INVENTION

This disclosure describes the development of a novel, low-impactapproach for the delivery of treatment amendments for contaminatedsediments. Unlike available delivery systems that rely on injection ormechanical mixing of the sediment, the low-cost and low-impact deliverysystem makes use of material engineering aided by natural mixing(bioturbation) processes to work treatment materials into thebiologically active sediment zone. An advantage of the low-impactdelivery system found over conventional systems is that it targets thebiologically active zone where the benthic organisms reside, and is lessdestructive of benthic habitats (the body of organisms living at thebottom of a body of water).

Research for the present invention demonstrates that agglomerates withthe desired characteristics can be produced and has shown that thetreatment material can be distributed through the biologically activezone in days to weeks, where benthic communities are established.Because the present delivery system depends on natural mixing processes,the application of the technology requires biological assessment of thesediment in order to judge efficacy and to estimate loading rates.

The agglomerate disclosed herein represents the first delivery methodfor remedial materials to sediment that does not require mechanicalmixing into sediment. The technology is applicable in areas where theapplication of current in situ treatment practices are problematic andexpensive, such as in deep water, in vegetated areas, in sensitivewetlands, or over very large areas. The agglomerates can be designed tocarry a number of remedial materials to sediment, allowing for in situtreatment of a variety of contaminants.

While the sediments and benthic organisms used in the model systems inthis study are representative of the Chesapeake Bay coastal sedimentsand Grasse River sediments, the treatment materials that have beendeveloped have wide application to myriad freshwater environments (e.g.lake Hartwell, Hudson River, Great Lakes Areas of Concern) as well asmarine estuarine/marine systems (e.g. Hunters point in San Francisco Bayor the Patapsco River and Baltimore Harbor in Maryland). Applicationmethods that can be considered at a conceptual level include, but arenot limited to, a barge-mounted broadcast-type fertilizer spreader andother methods such as some of those currently employed for thin-layercapping.

A primary element of the present system is the novel approach tocost-effective delivery of sediment amendments and utilization ofnatural processes to achieve mixing of the treatment amendments in thebioactive zone in sediments. A further new element of the invention isthe manipulation of material properties of the new amendment pellets (or“particles”) to achieve surprisingly efficient delivery through a watercolumn and controlled breakdown of the amendments while maintainingeffectiveness in sediment remediation.

Historically, the most commonly considered alternatives for contaminatesediment management are (1) dredging and placement of large volumes ofremoved sediment in confined disposal facilities (CDFs) or hazardouswaste landfills and (2) capping, an option for containment in engineeredsubaqueous sites. Removal options such as dredging and excavation havecertain clear advantages, especially in situations where hot spots existand there is a desire to reduce sources and risks quickly and to insurea permanent solution. However, the limitations and disadvantages ofthese methods have also become better understood. In particular, theissues of re-suspension of contaminants, residual contamination, and thedestruction of benthic habitat are concerns that arise when removaltechnologies are considered. In situ treatment of sediments can helpaddress the presence of residual contamination and, as proposed here,can be targeted at the surficial sediment layer of interest, andimplemented in a way that minimizes impact on native benthic andassociated fish and wildlife communities.

In situ treatment of contaminated sediment can be an especiallyattractive alternative for low or moderately contaminated sites. Thisnew alternative can be used by itself or in combination with othermethods. Remedial strategies that combine methods are expected to becomemore common. For example, in situ treatment could be part of a cappingtechnology, could be used to manage residual contaminants afterdredging, or could be used to enhance Monitored Natural Recover (MNR)processes. Being able to deliver in situ treatment in a low-impact(little negative effect) manner opens the possibility of using thistechnology to address more sensitive areas (for example where there aresea grass beds or a valued invertebrate prey base for fish and wildlife)and larger areas.

Accordingly, in keeping with the description herein the presentinvention is an agglomerate for use in economical bulk treatment ofcontaminated sediments with minimal environmental impact. Theagglomerate is formed from a sorbent, such as powdered activated carbon,for example, bentonite clay and sand. The agglomerate has sufficientdensity so as to sink through a water column into sediment below thewater column and is still sufficiently soft upon wetting as to becapable of mixing with the sediment when subjected only to bioturbation.The agglomerate can be formed into pellets and applied to a water columnover contaminated sediment by broadcast methods, so as to permiteconomical remediation of contaminated sediment with negligibleenvironmental impact.

The invention is further, briefly, a low-impact method of remediatingcontaminated sediments including the steps of a) providing anagglomerate formed of a sorbent, bentonite and sand and havingsufficient weight so as to sink through a water column into sedimentbelow the water column and still be sufficiently soft upon wetting as tobe capable of mixing with the sediment when subjected only tobioturbation; b) applying the agglomerate to the surface of a watercolumn having contaminated sediment there under; and c) permitting theagglomerate to sink through the water column and be subject tobioturbation; thereby economically decontaminating sediment with lowimpact on the benthic community in the sediment.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a delivery system constructed inaccordance with and embodying the present invention illustrating theapplication of tailored agglomerates that slowly break down and areincorporated into the biologically active zone of the treated sediment.

FIG. 2 is a photograph showing samples of produced agglomerates: a) 55%powdered activated carbon, 25% bentonite, 15% sand, 5% cellulose; and b)60% powdered activated carbon, 20% bentonite, and 20% sand.

FIG. 3 is a schematic chart of Iodine Number Test Results showingmilligrams of iodine adsorbed per gram of material.

FIG. 4 is a photograph showing, on the left, the placement of a layer ofpowdered activated carbon/bentonite/sand pellet on Grasse Riversediments and the, on the right, 3 days of activity of L. variegatesthat produced a layer of worm feces on top of the layer of pelletsstarting the process of slow incorporation of the amendment into the toplayer of sediments.

FIG. 5 is a close-up image of the sediment profile showing the buildupof worm feces (in 7 days) on top of the amendment pellets and the slowincorporation of the pellet materials through the worm burrows.

FIG. 6 is a photograph taken with ultraviolet light showing bioturbationtest control tank on Day 28, illustrating that marine sediments withoutorganisms show no mixing of the added fluorescent-tagged pellets intothe sediment layer.

FIG. 7 is a photograph of a bioturbation test activation tank on Day 28illustrating that marine sediment with Leptocheirus and Neris showsmixing of the added fluorescent-tagged pellets into the top two inchesof sediment. The scale at the left side of the photograph shows sedimentdepth in inches.

FIG. 8 is a chart illustrating the reduction of PCB bioaccumulation inbenthic organisms after amendment of sediment with 2% activated carbondelivered with and without the use of the new amendment pellettechnology. The results indicate that packaging of the carbon into thenew pellets does not adversely impact the reduction of PCBbioaccumulation in benthic organisms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

The present low-impact delivery system delivers treatment materialsdirectly to the water column and forgoes the more expensive alternativeof mechanical mixing and/or injection. Instead, the technology relies onnatural biomixing (bioturbation) processes mix treatment agents into thebiologically active zone as shown conceptually in FIG. 1. The technologyrelies on “packaging” and delivering the treatment agent within a densegranule that is able to resist re-suspension and that would be workedinto the sediment by the organisms, Many of the in situ treatment agentscurrently being evaluated for sediments (e.g., activated carbonparticles) do not have the desired properties to be delivered directlyfrom the water column. This research involved developing and testingvarious agglomerates with the following properties: dense enough to sinkthrough the water column and provide a light non-suffocating layer onthe sediment, dense enough to be resistant to re-suspension over theperiod it takes to be worked into the sediments, and able to break downto release active agents over the period of weeks to months. Inaddition, the binders used for the agglomerate must have negligibletoxicity. The clear advantages of this over conventional systems arethat it targets the biologically active zone where the benthic organismsreside, is less destructive of benthic habitats, and can be used toaugment removal and monitored natural restoration projects. Further,because the delivery system is relatively straight forward and has lowenvironmental impact, applications can be repeated, as needed over time.

The development of the agglomerate involved testing a variety ofmaterials for the ability to form the agglomerate using scalablelaboratory techniques, testing the physical characteristics of theresulting agglomerates, and testing the interaction of the activatedcarbon and other agglomerate additives. Agglomerates were developed withthe following properties: dense sediment, dense enough to be resistantto re-suspension over the period it takes to be worked into thesediments, and able to break down to release active agents over theperiod of days to weeks. The most promising formulation was made ofpowdered activated carbon, bentonite clay, and sand as shown in FIG. 2,and was produced in larger quantities for use in biological tests.Preferably the agglomerate is formed into pellet shapes of approximately1 mm to 15 mm in diameter. The pellets are preferably oblong orsubstantially spherical but may conceivably take other compact shapesand may conceivably be up to about 100 mm in length.

The prepared sorbent pellets were tested for friability by placing in aglass bottle and rolling at four rpm for one hour in a roller. This testwas used to compare the friability of the pellets made using differentformulations of binders. The amount of fines produced was to be measuredby sieving through a 1 mm sieve and weighing the fines. The amount offines produced form the different formulations tested are shown inTable 1. As shown in Table 1, the percent fines produced after one hourof tumbling was about 1% or less for the four formulations tested. Theuse of cellulose reduced the fines to less than 0.1%. Bentonite wasshown to be important as a binder because lowering the amount ofbentonite raised the percentage of particles broken off.

TABLE 1 Results of pellet friability test. % of Weight of pellets Weightof sieved pellets Pellet composition (%) before particles sieved off PACBentonite Sand Cellulose (g) (g) (%) 60 30 10 0 30    0.57    0.17 60 2020 0 26    0.31    1.03 60 25 15 0 30    0.29    0.97 60 25 10 5 30<0.1  <0.33

Example: The iodine number test (ASTM D 4607) was used to determine ifany of the binders or additives would render the activated carbonineffective. The tests used the iodine as a surrogate for other organicchemicals, such as PCBs (polychlorinated biphenyls), which are commonsediment contaminants. The results of the iodine number tests are shownin FIG. 3. The average amount (milligrams) of iodine adsorbed per gramof activated was 869 and 969 for one gram of activated carbon and twograms 50/50 of activated carbon/bentonite, respectively. These resultsindicate that bentonite does not interfere with the ability of activatedcarbon to adsorb iodine. The amount of iodine adsorbed was reduced whencellulose was used as a binder. The cellulose appears to produce agel-like layer over the carbon that hinders mass transfer or sorbate,reducing the apparent effectiveness of the carbon. In a fieldapplication the cellulose will gradually degrade or wash away, exposingthe sorbent materials slowly over time.

There was no observed sediment avoidance by the Lumbriculus worm. Theworms immediately burrowed into the sediment when placed in the testchamber. A t-test was performed on the data, and there was nosignificant difference between the test group containing sediment andun-agglomerated activated carbon or the test group containing sedimentand the agglomerate compared to the control group. The results indicatethat the agglomerate does not pose a threat to benthic organisms.

Example: Microcosm studies were conducted to evaluate the behavior offreshwater oligochaetes in sediment amended with activatedcarbon/bentonite/sand pellets. PCB-impacted sediment from Grasse River,N.Y. and the freshwater oligochaete Lumbriculus variegates were used inthese studies. Sediment (100 ml) and oligochaetes (25) were placed in400 ml glass beakers in triplicate. The control beakers containedsediment only and the treatment beakers had sediment covered withpellets at a does to achieve 2.5% activated carbon based on sediment dryweight. We observed active breakdown of the new pellets by the wormbioturbation activity. After just three days of introducing the worms,the top layer was covered with excreted sediments and the amendmentmaterial from the pellets was integrated into the sediment layer. Afterone month of worm activity the new sediment treatment pellets were notdistinguishable and the carbon delivered with the new pellets wasintegrated into the top two inch layers of sediment. FIG. 4 shows thesurface of sediment with pellets before the addition of the oligochaetesand after 3 days of bioturbation. A close-up image of the sedimentprofile shown in FIG. 4 illustrates the process of the breakdown of thepellets and incorporation into the bioactive layer of freshwatersediments.

Example: The process of bioturbation is illustrated in FIG. 5 showingthe buildup of worm feces on top of the added pellets on the sedimentsurface. To evaluate mixing, a fluorescent tracer material wasincorporated into the agglomerate. The experiment was designed to testthe ability of benthic organisms to mix the agglomerate and associatedtreatment materials into sediment by bioturbation (i.e. through naturalmovement and sediment irrigation processes).

The experiment was modeled after a 28-day bioaccumulation test, andincluded: three large (approximately 50 gallon) tanks containing teninches of sediment with a natural benthic community enhanced with boththe estuarine amphipod Leptocheirus and polyuchaete Nereis, and; threestandard (approximately 20 gallon) size tanks with sieved naturalsediment for the experimental control. Sieving removes the invertebratesresponsible for most of the sediment mixing via bioturbation processes.

The sediments used in the experiment were collected from the Wye Riverin Queen Annes County, Maryland. The Wye River is relatively clean ofcontamination, and is used as referenced sediment. Special agglomeratescontaining 5% by weight of a fluorescent tracer material were preparedfor the experiment. The fluorescent tracer allows for the movement ofthe agglomerate materials through sediment by bioturbation to beevaluated by fluorescence imaging of the sediment illuminated with anultraviolet lamp.

The agglomerates with the tracer were applied to the sediment surface ofthe test tanks and allowed to sit for 30 days. Observations were takenat the start of the experiment and repeated weekly. FIGS. 6 and 7 showrepresentative pictures of the control and active bioturbation testtanks under fluorescence at day 28 of the experiment, respectively. Thetank shown in FIG. 6, with an active benthic community, shows theincorporation of the fluorescent-tagged amendment into the top severalinches of the sediment. The amendment materials delivered with the newtreatment pellets was carried into the worm burrows and integrated intothe sediment top layer through the bioturbation activity of the worms.Thus, delivery of sediment amendments in the form of the new pellets andallowing benthic organism activity to mix the amendment pellets is amore efficient method of delivering the amendments to the locations theyare most needed, which is the natural habitat of the base of the aquaticfood chain.

Example: The effect of activated carbon delivered to sediment with andwithout the use of the new amendment pellet technology was tested usingfreshwater sediments impacted with polychlorinated biphenyls (PCBs). Thestudy sediment was obtained from Grasse River, N.Y., that has beenimpacted with PCBs from historic industrial activities. A freshwateroligochaete, L. variegates, was used as a test organism to measurebioaccumulation of PCBs. The bioaccumulation study was based on theUSEPA Methods for Measuring the Toxicity and Bioaccumulation ofSediment-Associated Contaminates with Freshwater Invertebrates. Theexperiment was set up in 250 ml glass beakers containing approximately100 ml of wet sediment and about 0.5 g of worms. The control experimentreceived sediment with no treatment materials. The first treatmentinvolved placing a layer of activated carbon (approximately 2% by dryweight of sediment) on the top of the sediment without mixing. Thesecond treatment involved placement of the same amount of activatedcarbon (about 2%) in the form of the new treatment pellets.

Each of the two treatments and the control experiment had five replicatebeakers. The amendments were allowed to remain on the sediment for aweek before the introduction of the worms. The worms were exposed to thetreated or untreated sediments for 28 days. At the end of the exposureperiod, the worms were removed from the sediment, depurated for 8 hours,weighed, and extracted for analysis of PCB residue in the tissue. Asshown in FIG. 8, there was a significant reduction of PCBbioaccumulation in the worms in the treated samples, especially for themono through pentachlorobiphenyls. Total PCB bio-uptake reduction was54% for the activated carbon treated sediment and 56% for the case whereactivated carbon was delivered as the new pellets. There is nostatistical difference between the application of activated carbon withand without the use of the new pellet technology. The results indicatethat packaging of the carbon into the new pellets does not adverselyimpact the reduction of PCB bioaccumulation in the organism. Theeffectiveness of the application is expected to improve with longercontact of the amendments with contaminated sediment.

FIG. 8 illustrates a reduction of PCB bioaccumulation in benthicorganisms after amendment of the sediment with 2% activated carbondelivered with and without the use of the new pellet technology. Theresults indicate that packaging of the carbon into the pellets does notadversely impact the reduction of PCB bioaccumulation in the organisms.

The average cost of PCB contaminated sediment remediation based ondredging and disposal carried out at nineteen areas of concern in theGreat Lakes basin is approximately $187 million. A higher cost of about$256 million is expected for the dredging and disposal of PCBcontaminated sediment in the ongoing Hudson River cleanup effort.Assuming a typical dredging depth of three feet, the remediation costper square yard is approximately $200.

It is anticipated that for the new amendment pellet approach theapplication cost will be small due to the lack of sediment handling,transport, and disposal costs. The main cost in our approach will be thematerial cost of the amendments to the pellets. The material cost forpowdered activated carbon is approximately $1/pound and even less forregenerated carbon. It is further anticipated that forming into pelletsmay increase the cost to about $2/pound. The application rate based onour previous work is typically in the range of three to five pounds persquare yard, to remediate the top six inches of sediment that comprisesthe bioactive zone. Thus, with our approach, the sediment remediationcost is in the range of $10 per square yard, which is less than an orderof magnitude compared to traditional dredging costs. The cost of fieldapplication of the proposed technology is expected to be low primarilybecause of the low cost of the sorbent material and because this is anin situ process not involving any sediment relocation. Thus, a roughestimate of the material costs for the stabilization process is veryattractive. The material cost compares very favorably with the cost ofcurrently used disposal options.

Accordingly it will be understood and appreciated that the presentapproach is a highly desirable, cost-effective delivery of sedimentamendments and utilization of natural processes to achieve mixing of theamendments in the bioactive zone in the sediments. We have also hereindisclosed a new approach in the manipulation of material properties ofthe amendment pellets to achieve efficient delivery through a watercolumn and controlled breakdown of the amendments while maintainingeffectiveness in sediment remediation.

As various modifications could be made to the exemplary embodiments, asdescribed above with reference to the corresponding illustrations,without departing from the scope of the invention, it is intended thatall matter contained in the foregoing description and shown in theaccompanying drawings shall be interpreted as illustrative rather thanlimiting.

Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims appended heretoand their equivalents. As examples only, and not limitations, possiblevariations in the new system can include: i. use of different types ofsorbent amendment materials for organic and metal contaminants; ii. useof different types of reactive amendment materials; and iii. use ofdifferent types of biologically active amendment materials.

1-21. (canceled)
 22. An agglomerate for treating contaminated sedimentsbeneath a body of water comprising: a sorbent and a binder; said sorbentand said binder being agglomerated into particles; said particles beingdense enough to sink in water without re-suspension in the water of saidsorbent after said agglomerate particles are distributed on a surface ofa body of water over contaminated sediment; said particles breaking downin sediment beneath the body of water under only the influence ofbioturbation; whereby said sorbent is exposed to contaminants in thesediment, beneath the water.
 23. The agglomerate of claim 22 furthercomprising a dense element being agglomerated in said particles.
 24. Theagglomerate of claim 23 further comprising said dense element beingsand.
 25. The agglomerate of claim 22 further comprising said sorbentbeing activated charcoal carbon.
 26. The agglomerate of claim 22 furthercomprising said binder being bentonite.
 27. The agglomerate of claim 22,wherein said particles contain about 30% to about 80% sorbent.
 28. Theagglomerate of claim 22, wherein said particles contain about 10% toabout 30% bentonite clay.
 29. The agglomerate of claim 22, wherein saidbinder is bentonite clay, said sorbent is powdered activated carbon andsaid bentonite clay does not inhibit the ability of said powderedactivated carbon in the agglomerate to absorb iodine.
 30. Theagglomerate of claim 22, wherein the particles contain about 60%powdered activated carbon, about 20% bentonite clay and about 20% sand.31. The agglomerate of claim 22, wherein the particles contain about 0%to about 40% sand.
 32. The agglomerate of claim 22, and furthercomprising a binder having negligible toxicity to the benthic organismsso as to be suitable for repeat application to the same water column ifdesired.
 33. The agglomerate of claim 22, further comprising saidparticles having cellulose.
 34. The agglomerate of claim 22, furthercomprising said break down of said agglomerate delivering said sorbentto a bioactive zone of sediment for sorption of contaminants.
 35. Theagglomerate of claim 22, further comprising said agglomerate producingno more than one percent by weight of fines when the agglomerate isrolled for one hour at four rpm.
 36. The agglomerate of claim 22,wherein said particles are formed in the size range of about 1 mm toabout 15 mm in diameter.
 37. The agglomerate of claim 22, wherein saidparticles have a length of up to about 100 mm.
 38. The agglomerate ofclaim 22 further comprising said particles having a consistency of about55% powdered activated carbon, about 25% bentonite, about 15% sand andabout 5% cellulose.
 39. The agglomerate of claim 22 further comprisingsaid particles having a consistency of about 60% powdered activatedcarbon, about 20% bentonite and about 20% sand.
 40. The agglomerate ofclaim 22 further comprising said sorbent treating metal contaminantsfrom the sediment.
 41. The agglomerate of claim 22 further comprisingsaid sorbent treating organic contaminants from the sediment.
 42. Theagglomerate of claim 22 wherein said sorbent is exposed to contaminantsin a benthic zone of the sediment wherein mixing by bioturbation takesplace.
 43. The agglomerate of claim 22 wherein said particles have adensity insufficient to penetrate bottom sediment after sinking so thatsaid particles are available to be mixed by bioturbation.
 44. Theagglomerate of claim 22 wherein said particles settle on a surface ofthe sediment.
 45. The agglomerate of claim 22 wherein said sorbent isexposed to contaminants in a biologically active zone of the sedimentwhere bioturbation occurs.
 46. The agglomerate of claim 45 wherein saidbiologically active zone of the sediment is substantially about 6 inchesdeep.
 47. The agglomerate of claim 45 wherein said biologically activezone of the sediment is substantially about 2 inches deep.
 48. Theagglomerate of claim 44 wherein said particles form a light, nonsuffocating and temporary layer on the sediment and said particles arebroken down and mixed by bioturbation.
 49. The agglomerate claim 33wherein said cellulose acts as a degradable binder to hold the particletogether during application.
 50. The agglomerate of claim 22 whereinsaid particles are pellets.
 51. The agglomerate of claim 22 wherein saidparticles sink to a region where bioturbation occurs.